The answer is the compute.subnetworks.use permission on the host project subnet. This permission is required because when a service project administrator attempts to create a VM using a specific subnet from the Shared VPC host project, the service project itself does not own that subnet; the host project must explicitly grant the right to use it. Without this permission, the operation fails with a compute.subnetworks.use permission error, even if the user has broader network or instance creation roles. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of Shared VPC IAM delegation, where permissions are inherited from the host project, not the service project. A common trap is confusing compute.networks.use (needed for the VPC network itself) with the more granular compute.subnetworks.use (needed for a specific subnet). Remember the mnemonic: "Subnet use, subnet choose" — you need the subnet-level permission to pick the subnet for your VM.
PCNE Implementing a Virtual Private Cloud Practice Question
This PCNE practice question tests your understanding of implementing a virtual private cloud. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company uses Shared VPC with a host project and multiple service projects. A service project administrator wants to create a VM with an internal IP from a specific subnet in the host project. The operation fails with a permission error. What is the most likely missing permission?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
compute.subnetworks.use on the host project subnet.
Option D is correct because the service project needs the compute.subnetworks.use permission on the specific subnet in the host project. This permission is part of the roles/compute.networkUser role. Option A is incorrect because compute.networks.use is needed for using the VPC network, but the error is more specific to subnet use. Option B is incorrect because compute.instances.create is for creating instances, not for using a subnet. Option C is incorrect because resourcemanager.projects.get is not related to subnet usage.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
resourcemanager.projects.get on the host project.
Why it's wrong here
Not related to subnet usage.
✓
compute.subnetworks.use on the host project subnet.
Why this is correct
This permission grants use of a specific subnet.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
This is needed for instance creation but not for subnet use.
✗
compute.networks.use on the host project VPC.
Why it's wrong here
This permission is also required but the error usually points to subnet use first.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related PCNE subnetting questions on CIDR, address ranges, and subnet selection.
Implementing a Virtual Private Cloud — This question tests Implementing a Virtual Private Cloud — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: compute.subnetworks.use on the host project subnet. — Option D is correct because the service project needs the compute.subnetworks.use permission on the specific subnet in the host project. This permission is part of the roles/compute.networkUser role. Option A is incorrect because compute.networks.use is needed for using the VPC network, but the error is more specific to subnet use. Option B is incorrect because compute.instances.create is for creating instances, not for using a subnet. Option C is incorrect because resourcemanager.projects.get is not related to subnet usage.
What should I do if I get this PCNE question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related PCNE subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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